Threshold values are used for signal detection and for decision processes in a multiplicity of signal processing devices. By way of example, the signal power or a processing variable derived therefrom is tested against a prescribed value—the threshold value. Depending on whether the processing variable exceeds the threshold value, a signal is considered to have been detected or a particular decision is made.
By way of example, a threshold value decision can be used to test whether a received signal contains useful data. Normally, these useful data have superimposed disturbances (noise, interference) and need to be separated from these disturbances. By way of example, the received signal is processed in suitable fashion in a radio receiver (e.g., using a correlator) and the processing value is compared with a threshold value. If the processing value exceeds this threshold value, the useful signal is considered to have been detected. Otherwise, it is assumed that the received signal contains exclusively disturbance components.
A considerable drawback of threshold-value-based decisions is the dependency of the decision quality on the average received signal power, since absolute values are compared with one another. The received signal power may fluctuate considerably, however, for example as a result of switching by amplifier stages connected upstream. It thus becomes necessary to adapt the threshold values to the average power of the signal that is to be processed or to be tested.
FIG. 1 shows the normal approach of a signal processing device based on threshold value decisions. An input signal s is subjected to various signal processing procedures in various signal processing stages 1, 2, . . . , N. The respective signal processing stages have detectors 1.1, 2.1, . . . , N.1 connected downstream of them which test the processing signal which is output by the respective signal processing stage 1, 2, . . . N. The test is performed by comparing the processing signal with a respective threshold value. The respective threshold value is made available to the detector 1.1, 2.1, . . . , N.1 by a local threshold value generation stage 1.2, 2.2, . . . , N.2. For the requisite threshold value adaptation, local threshold value adaptation stages 1.3, 2.3, . . . , N.3 are provided which accept the respective processing signal at their input and make a correction value available at their output. The threshold-value-based correction value is supplied to the respective downstream threshold value generation stage 1.2, 2.2, . . . , N.2 via an interface. A result processing section connected downstream of the detectors 1.1, 2.1, . . . , N.1 evaluates the threshold value comparison results obtained from the detectors, manages them and then stipulates the further signal processing.
The local threshold value adaptation shown in FIG. 1 works perfectly in terms of function, but has the drawback that calculation of the adaptation values which are output by the threshold value adaptation stages 1.3, 2.3, . . . , N.3 requires a high level of involvement overall. Although the processing signals which are output by the signal processing stages 1, 2, . . . N are normally different, the usually very complex calculations of the adaptation values in the system are performed a plurality of times at least for some of the computation cycles. This firstly increases the circuit's power consumption and secondly results in an increased surface area requirement for the circuit on account of the high level of circuit complexity.